As you may already know, Mathematica is a wonderful piece of software.
However, it has a few characteristics that tend to confuse new (and sometimes not-so-new) users. That can be clearly seen from the the fact that the same questions keep being posted at this site over and over.
Please help me to identify and explain those pitfalls.
Suggestions for posting answers:
- One topic per answer
- Focus on non-advanced uses (it's intended to be useful for beginners and as a question closing reference)
- Include a self explanatory title in h2 style
- Explain the symptoms, the mechanism behind the scenes and all possible causes and solutions you can think of. Be sure to include a beginner's level explanation (and a more advance one too, if you're in the mood)
- Include a link to your answer by editing the Index below (for quick reference)
- Attempting to make an assignment to the argument of a function
- Avoiding loops
- Basic syntax issues
- Learn how to use the Documentation Center effectively
- Lingering Definitions: when calculations go bad
- The displayed form may substantially differ from the internal form
- Understanding what Set (=) really does
- Understand that semicolon (;) is not a delimiter
- Understand the difference between exact and approximate (Real) numbers
- Understand the difference between Set (or =) and SetDelayed (or :=)
- User-defined functions, numerical approximation, and NumericQ
- Using the result of functions that return replacement rules
- What the @#%^&*?! do all those funny signs mean?
- Why is my picture upside-down?